Istaq Ahmed

In situ high temperature powder neutron diffraction study of undoped and Ca-doped La28−xW4+xO54+3x/2 (x = 0.85)

In situ neutron diffraction experiments of 2% Ca-doped and nominally undoped lanthanum tungstate (La28-xW4+xO54+3x/2, with x = 0.85) have been carried out under controlled pD(2)O and pO(2) at elevated temperatures. All the diffraction patterns could be refined using an average cubic fluorite-related structure, in accordance with recent reports. The material exhibits disorder of the oxygen and the cation sublattices. Splitting of the oxygen sites around tungsten from the 32f to 96k Wyckoff position in the Fm (3) over barm space group improves the model and can better represent the oxygen disorder. No phase transition was detected from room temperature up to 800 degrees C under any of the studied conditions. Expansion of the unit cell constants in the presence of water at intermediate and low temperatures was correlated with the formation of protonic defects. The thermal expansion coefficient for lanthanum tungstate is rather linear under all studied conditions (similar to 11 x 10(-6) K-1). The in situ diffraction studies are correlated with dilatometry investigations and conductivity measurements.

Endoscopic sutured closure of a gastric natural orifice transluminal endoscopic surgery access gastrotomy compared with open surgical closure in a porcine model. A randomized, multicenter controlled trial

BACKGROUND AND STUDY AIMS In natural orifice transluminal endoscopic surgery (NOTES) procedures it is essential to be able to perform secure closure of the access perforation. The aim of this study was to compare endoscopically sutured closure of a gastric access gastrotomy using the tissue apposition system (TAS), with closure via laparotomy in a randomized multicenter study. METHODS A total of 32 pigs (18 - 42 kg) were used in this study. The gastric NOTES access was created using a needle knife and a 20-mm balloon. Following transgastric pelvic peritoneoscopy, the endoscope was withdrawn into the stomach. The animals were then randomized to endoscopic closure or laparotomy with surgical closure. Procedure time, recovery time, and weight gain were measured. At necropsy, adhesions, abscesses or peritonitis were recorded. RESULTS Of the 32 pigs, 29 survived 14 days without complications. All endoscopic and all open surgical closures were secure at postmortem. On average two suture pairs were used for endoscopic closure. Surgical closure was quicker (12.5 vs. 20.1 minutes). Recovery time and postoperative weight gain were similar for both groups. Two pigs in the endoscopic group died: one of gastric dilatation, without leakage from the gastrotomy; another was euthanized due to rectal prolapse. In the laparotomy group one pig was euthanized after 7 days due to abdominal wound dehiscence. At necropsy there were significantly more intra-abdominal adhesions in the laparotomized group. CONCLUSION This randomized controlled study of endoscopic and surgical closure of a gastrotomy made for transperitoneal access for NOTES procedures suggests that both techniques are comparable in technical closure rates, postoperative recovery, and prevention of peritonitis. There were fewer adhesions in the endoscopic group.

Proton conduction in Perovskite Oxide BaZr0.5Yb0.5O3-δ Prepared by Wet Chemical Route

A wet chemical route has been used to synthesize the oxygen deficient perovskite BaZr 0.5 Yb 0.5 O 3-δ . Analysis of X-ray powder diffraction data showed that both dried and hydrated samples adopt cubic crystal structures of space group Pm3m. Dynamic thermogravimetric analysis showed a significant mass loss for the hydrated sample compared to the dried sample, indicating that ∼28% of the oxygen vacancies are filled by protonic defects. The strong O-H stretch band, 2500-3500 cm -1 , in the IR absorbance spectrum also clearly manifests the presence of significant levels of protons in the hydrated material. Proton conductivity was investigated on prehydrated (under dry Ar) and as-prepared (under wet Ar) samples. The heating cycle of the prehydrated sample showed higher proton conductivity compared to the cooling cycle, especially in the intermediate temperature range (150-550°C). Finally, comparison with data for BaZr 0.9 Yb 0.1 O 3-δ revealed that the more heavily doped sample showed higher proton conductivity compared to the more lightly doped sample.

Proton Conduction in Perovskite Oxide BaZr0.5Yb0.5O3 − δ Prepared by Wet Chemical Synthesis Route

A wet chemical route has been used to synthesize the oxygen deficient perovskite BaZr 0.5 Yb 0.5 O 3-δ . Analysis of X-ray powder diffraction data showed that both dried and hydrated samples adopt cubic crystal structures of space group Pm3m. Dynamic thermogravimetric analysis showed a significant mass loss for the hydrated sample compared to the dried sample, indicating that ∼28% of the oxygen vacancies are filled by protonic defects. The strong O-H stretch band, 2500-3500 cm -1 , in the IR absorbance spectrum also clearly manifests the presence of significant levels of protons in the hydrated material. Proton conductivity was investigated on prehydrated (under dry Ar) and as-prepared (under wet Ar) samples. The heating cycle of the prehydrated sample showed higher proton conductivity compared to the cooling cycle, especially in the intermediate temperature range (150-550°C). Finally, comparison with data for BaZr 0.9 Yb 0.1 O 3-δ revealed that the more heavily doped sample showed higher proton conductivity compared to the more lightly doped sample.

Proton Conductivity in Mixed B-Site Doped Perovskite Oxide BaZr[sub 0.5]In[sub 0.25]Yb[sub 0.25]O[sub 3 - delta]

A wet chemical route was used to prepare the oxygen deficient codoped perovskite oxide BaZr0.5In0.25Yb0.25O3−. Analysis of X-ray powder diffraction data showed that the sample belongs to the cubic crystal system with space group Pmm. Dynamic thermogravimetric (TG) analysis confirmed complete filling of oxygen vacancies (V) by protonic defects (OH) during the hydration process. The proton conductivity was investigated by impedance spectroscopy. The bulk and total conductivities of prehydrated BaZr0.5In0.25Yb0.25O3− were found to be 8.5×10−4 and 2.2×10−5 S cm−1, respectively, at 300°C. The total conductivity in the codoped perovskite oxide was higher compared to that of the respective single doped perovskite oxides with the same doping level. The bulk and grain-boundary mobility and diffusion coefficients of protons were calculated at 200°C using impedance and TG data to obtain the conductivity and proton concentration, respectively. The high bulk diffusivity (2.3×10−7 cm2 s−1) was obtained which indicates that the protons are more free to move in the heavily doped matrix compared to the lightly doped systems where trapping of protons occurs.

An animal model for studying endoscopic ultrasound changes of early chronic pancreatitis with histologic correlation: A pilot study

BACKGROUND AND STUDY AIMS Due to the difficulty in obtaining pancreatic tissue for histology in humans, we developed an animal model for studying endoscopic ultrasound (EUS) changes of early chronic pancreatitis. This report on the animal model describes the serial changes of early chronic pancreatitis by EUS and correlates results with histology. MATERIALS AND METHODS Four 60 - 80-lb dogs were used in the study. Pancreatic EUS was performed to provide baseline images prior to any procedure. At laparotomy, a guide wire was passed into the pancreatic duct, and a 5-Fr pancreatic stent was introduced over the wire into the pancreatic duct. Animals were divided into two survival groups - 2 weeks and 4 weeks. In each group, EUS examination was performed under anesthesia to image the pancreas and then followed by euthanasia. Sequential pancreatic sections were taken from the head, body, and tail of the pancreas. EUS findings were correlated with histologic results with respect to degree of fibrosis, inflammation, and edema. RESULTS At baseline EUS, the pancreas appeared homogeneous with only a few echogenic septations and echogenic margins of the main pancreatic duct. At 2 and 4 weeks poststenting, EUS images showed the following changes: lobularity, hyper and hypoechoic foci, increased echogenic septations, visible pancreatic duct side branches, and irregular margins of the main pancreatic duct. CONCLUSIONS The dog model for chronic pancreatitis appears to be a promising method for studying sequential changes of chronic pancreatitis by EUS and correlating results with histology.

Improved Proton Conductivity in Spark-Plasma Sintered Dense Ceramic BaZr0.5In0.5O3-delta

Spark-plasma sintering method was used to prepare dense proton conducting perovskite oxide BaZr0.5In0.5O3-delta. Analysis of X-ray powder diffraction data showed that the sample adopt the cubic crystal structure having the space group Pm3m. Thermogravimetric analysis of prehydrated samples showed significant mass losses beyond 300 degrees C due to loss of protons as water vapor. Scanning electron microscope images show that the grain size of the spark-plasma sintered dense sample was smaller than that of solid-state sintered porous sample. The highest total proton conductivity (2 X 10(-3) S cm(-1) at 450 degrees C) was found for dense spark-plasma sintered sample under wet H-2 than the samples prepared by other routes.

Synthesis and Enhanced Proton Conduction in a 20 mol% Ytterbium Doped Barium Zirconate Ceramic Using Zn as Sintering Aid

20% Ytterbium (III)-doped perovskite structured barium zirconate, BaZrO3, was prepared by two different synthesis routes: solid state and sol-gel routes. 2 % Zinc (II) was added as an acceptor dopant at the Zr (IV) site according to stoichiometry. It was also added as 2 % excess of the formula. The purpose of this study is to see how zinc (II) acts as a sintering aid in view of synthesis route, densification and conductivity of the material. A dense ceramic (90% of theoretical density) was achieved by the sol-gel method when stoichiometry was adjusted. Phase purity of the samples was checked by X-ray powder diffraction (XRD). Thermogravimetric analysis (TGA) and Impedance spectroscopy (IS) was used to characterize hydration and electrical conductivity respectively.The data shows that the addition of stoichiometric amounts of Zn2+ via sol-gel synthesis route promotes not only densification but also water incorporation and conductivity in comparison with the solid state route, keeping the same final sintering temperature of 1500°C. For example, pre-hydrated BaZr0.78Zn0.02Yb0.2O3-δ, prepared via the sol-gel method shows total conductivity (σtot) value of 3.14*10-5 and 3.8*10-3Scm-1, whereas for the solid state route, σtot values are 1.74*10-5 and 8.87*10-4Scm-1 under dry Ar (heating cycle) at 300° C and 600° C, respectively.